Glossing an image printed on a substrate generally improves the perceived quality of the image. Colors in the image are brighter and better defined after glossing and generally the overall impression of the image is more appealing. Glossing is therefore frequently used in the production of printed images.
A gloss finish can be imparted to an image printed on paper by calendering. In calendering, the paper with the printed image is passed through the nip of a highly polished chrome finished roller, hereinafter referred to as a “calendering roller”, and a backing roller against which the calendering roller is pressed. (The backing roller may also be a calendering roller, if for example the paper is printed on both sides.) Calendering impresses the smooth surface finish of the calendering roller onto the colorants used to print the image, smoothing the surface of the colorants and giving them a gloss.
The final gloss of a printed image may be affected by the colorants used to print the image and the finish of the paper on which the image is printed. Whereas in general the gloss improves the perceived quality of the image, in some cases glossing results in undesirable “gloss contrast” between printed regions of the image and non-printed regions of the image. For example, when an image is printed on paper with conventional powder toner, a relatively thick layer of the toner is deposited on printed regions of the paper. If the image is glossed, the gloss of the toner is increased and all regions of the paper covered with toner acquire a high, substantially uniform gloss that is relatively independent of the gloss of the paper on which the image is printed. Non-printed regions of the paper are substantially unaffected by the glossing, and, if the paper gloss is low, can contrast substantially with the printed regions of the paper and reduce the perceived quality of the image. It should be noted that in some cases the printed toner is so thick that when fixed, pressure and hear applied to the image during fixing glosses the image.
Alternatively, and more conventionally images are glossed by coating the image with lacquer or varnish or laminating it with a film. These processes are complicated and expensive.